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Prime Movers to Transmitters.              479

A unit of heat will raise i Ib. of water through i Fahr. when near
39, its greatest density; and Dr. Joule found by experiment that

One unit of heat = 772-55 foot pounds of mechanical energy.

The number 772 therefore is spoken of as Joule's equivalent (J).
(See Appendix III., p. 930.)

Electrical energy may be estimated in terms of mechanical
energy as follows :

Energy in foot pounds = 737 E Q.

where E = Electro-motive force in volts.          l

and   Q = Quantity in coulombs.   (See App. ///.,/. 926).

Lastly, Chemical energy is measured by its heating effect,
found by careful experiment. Thus, i Ib. of good dry bituminous
coal will give out 14,500 units of heat when completely burnt,
which may be further represented in foot pounds.

Prime Movers are machines which obtain Nature's energy
at first hand for transmission of, or transformation into mechanical
energy. Such are: Heat Engines, Water-Wheels and Turbines,
Windmills, Electric Engines,* and Tidal Motors.

Power is direct or controlled energy, as distinguished from
the free energy of Nature or that, say, of a bullet The term has
been more usually applied to mechanical energy or the mechanical
equivalent of other energies, but is gradually being restricted to
indicate 'rate of doing work,' one horse-power being the unit

Transmitters of Power remove the mechanical energy
of a prime mover to a distance, or change the components and
perhaps the whole form of the energy. The following is a list:

, Lingerie:                    {

Shaft*                          i Lines   of shafting,  with   clutches,

2<     :    m^*                      |    couplings, and bearings.

3.  Spur gearing:              ,    For connecting parallel shafts.

4.  Bevel gearing:                Connecting shafts at various angles.

5.  Worm gearing:               Connecting shafts at right angles.

4   ti ,    '    *.                      ( Connecting shafts at various angles,

6.  Beltgearmg:            .   j     but chie|y paralleL               *

7.  Rope gearing (cotton);    For high speeds. :

* By voltaic battery or thermopile*